Voltage regulator having a plurality of capacitors configured to obtain a feedback voltage from a division voltage

ABSTRACT

An electronic circuit is provided. An error amplifier comprises a first input terminal coupled to a reference voltage, a second input terminal coupled to a feedback voltage, and a transistor comprises a first terminal coupled to an input voltage, a control terminal coupled to an output terminal of the error amplifier and a second terminal outputting an output voltage. A switching-capacitor circuit is coupled between the output voltage and the error amplifier and comprises a plurality of switching elements and at least first and second capacitors. The switching elements are switched by non-overlapping clocks such that the second capacitor is discharged to a bias voltage during a first period, and the first and second capacitors are connected together during a second period thereby extracting a division voltage from the output voltage to serve as the feedback voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to voltage regulators, and in particular tovoltage regulators using switching elements and capacitors to serve as afeedback resistor.

2. Description of the Related Art

Power management control systems including voltage regulators areincorporated within portable electronic devices, such as laptopcomputers, hand-held electronic devices, and cellular phones, togenerate a stable output voltage from a varying input voltage supply.The purpose of the voltage regulator is to regulate the external powersupplied to the internal circuitry for efficient current usage orquiescent power. The useable operating voltage is called the “drop-out”voltage, which is the difference between the input and output voltagesof regulator regulation. The smaller the difference, the more efficientthe system. Additionally, batteries can supply only a finite amount ofcharge, so, the more quiescent current the regulator uses, the lessoperating lifespan the battery will have and therefore the system willbe less efficient.

BRIEF SUMMARY OF THE INVENTION

Embodiments of an electronic circuit are provided, in which a voltageregulation unit converts an input voltage to an output voltage bycomparing a reference voltage and a feedback voltage. Additionally, aswitching-capacitor circuit is coupled between the output voltage andthe voltage regulation unit and comprises a plurality of switchingelements and at least first and second capacitors. The first and secondcapacitor extracts a division voltage from the output voltage by chargesharing between the first and second capacitors to obtain the feedbackvoltage.

The invention provides an embodiment of an electronic circuit, in whicha voltage regulation unit converts an input voltage to an output voltageby comparing a reference voltage and a feedback voltage, a firstcapacitor comprises a first terminal coupled to the output voltage, afirst switching element comprises a first terminal coupled to the firstterminal of the first capacitor and a second terminal coupled to asecond terminal of the first capacitor, and a second switching elementcomprises a first terminal coupled to the second terminal of the firstcapacitor and the second terminal of the first switching element, and asecond terminal coupled to the voltage regulation unit. A thirdswitching element comprises a first terminal coupled to the secondterminal of the second switching element, a second capacitor comprises afirst terminal coupled to a second terminal of the third switchingelement, and a second terminal coupled to a ground voltage, and a fourthswitching element comprises a first terminal coupled to a first terminalof the second capacitor and the second terminal of the third switchingelement and a second terminal coupled to the ground voltage.

The invention provides an embodiment of an electronic circuit, in whicha voltage regulation unit converts an input voltage to an output voltageby comparing a reference voltage and a feedback voltage, a firstswitching element comprises a first terminal coupled to the outputvoltage, a first capacitor comprising a first terminal coupled to asecond terminal of the first switching element and a second terminalcoupled to a ground voltage, and a second switching element comprises afirst terminal coupled to the first terminal of the first capacitor andthe second terminal of the first switching element. A second capacitorcomprises a first terminal coupled to a second terminal of the secondswitching element and a second terminal coupled to the ground voltage, athird switching element comprises a first terminal coupled to the secondterminal of the second switching element and the first terminal of thesecond capacitor and a second terminal coupled to the ground voltage,and a fourth switching element comprises a first terminal coupled to thefirst terminal of the first capacitor and the second terminal of thefirst switching element and a second terminal coupled to the voltageregulation unit.

The invention provides an embodiment of a voltage regulator, in which anerror amplifier comprises a first input terminal coupled to a referencevoltage, a second input terminal coupled to a feedback voltage, and atransistor comprises a first terminal coupled to an input voltage, acontrol terminal coupled to an output terminal of the error amplifierand a second terminal outputting an output voltage. Aswitching-capacitor circuit is coupled between the output voltage andthe error amplifier and comprises a plurality of switching elements andat least first and second capacitors. The switching elements areswitched by non-overlapping clocks such that the second capacitor isdischarged to a ground voltage during a first period, and the first andsecond capacitors are connected together during a second period therebyextracting a division voltage of the output voltage to serve as thefeedback voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows an embodiment of a voltage regulator;

FIG. 2 shows a diagram of a voltage regulator;

FIG. 3 shows another embodiment of a voltage regulator;

FIG. 4 shows a control timing chart of the switching elements in theswitching-capacitor circuit shown in FIG. 3;

FIG. 5 shows another embodiment of the voltage regulator;

FIG. 6 shows a control timing chart of the switching elements in theswitching-capacitor circuit shown in FIG. 5;

FIG. 7 shows another embodiment of a voltage regulator;

FIG. 8 shows another embodiment of a voltage regulator; and

FIG. 9 shows a control timing chart of the switching elements in theswitching-capacitor circuit shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 1 shows an embodiment of a voltage regulator. As shown, the voltageregulator 100 can be a low drop-out (LDO) voltage regulator or a lowquiescent current regulator and comprises an error amplifier EA0, a PMOSpass transistor M0 and a feedback resistor series 10 having a resistorseries (i.e., resistors R1 and R2). When the output voltage Vout isdesigned to be larger than a predetermined voltage level and the currentthrough the resistors R1 and R2 are limited, resistances of the resistorseries (R1 and R2) are required to be very large such that the layoutarea thereof is accordingly increased. For example, when the outputvoltage Vout is designed to be 2.8V and the current through theresistors R1 and R2 are limited at 0.5 μA, the total resistance of theresistors R1 and R2 is required to be 5.6MΩ. Generally, a powermanagement IC comprises more than 10 LDO voltage regulators, and thus,the feedback resistor series in all LDO voltage regulators would occupyan overwhelming majority of layout area when considering required lowcurrent.

In order to reduce layout are of such LDO voltage regulators in thepower management IC, embodiments of the invention utilize aswitching-capacitor (SC) circuit to be implemented as the feedbackresistor.

FIG. 2 shows a diagram of a voltage regulator. As shown, voltageregulator 200 comprises a voltage regulator unit 20 and aswitching-capacitor (SC) circuit 30. For example, the voltage regulator20 can be a low quiescent current regulator, a charge-pump circuit, aswitching-mode power supply or a low drop-out (LDO) voltage regulator,but is not limited thereto. The voltage regulator unit 20 converts aninput voltage Vdd to an output voltage Vout by comparing a referencevoltage Vref and a feedback voltage Vbk. The switching-capacitor circuit30 is coupled between the output voltage Vout and the voltage regulationunit 20 and comprises a plurality of switching elements and at least twocapacitors (shown in following figures). The switching elements in theswitching-capacitor circuit 30 are switched by non-overlapping clockssuch that one capacitor is discharged to a bias voltage during a firstperiod, and the two capacitors are connected together during a secondperiod thereby obtaining a division voltage of the output voltage Voutand serving as the feedback voltage Vbk. Namely, the switching-capacitorcircuit 30 performs a voltage-division to the output voltage Vout bycharge sharing between the two capacitors to obtain the feedback voltageVbk.

For example, the switching elements in the switching-capacitor circuit30 are switched such that two terminals of one of the two capacitors arecoupled to the output voltage Vout during a first period and the twocapacitors are connected in series during a second period to obtain thedivision voltage of the output voltage Vout and serve as the feedbackvoltage Vbk. Alternatively, the switching elements in theswitching-capacitor circuit are switched such that one of the twocapacitors is charged by the output voltage Vout during a first period,and the two capacitors are connected in parallel to obtain the divisionvoltage of the output voltage Vout and serve as the feedback voltage Vbkduring the second period.

FIG. 3 shows another embodiment of a voltage regulator. As shown, avoltage regulator 300 comprises a voltage regulation unit 20″ convertingthe input voltage Vdd to the output voltage Vout and aswitching-capacitor circuit 30A providing the feedback voltage Vbk tothe voltage regulation unit 20″ according to the output voltage Vout.The voltage regulation unit 20″ comprises an error amplifier EA1 and aPMOS pass transistor M1. The error amplifier EA1 comprises a first inputterminal coupled to the reference voltage Vref, a second input terminalcoupled to the feedback voltage Vbk, and an output terminal coupled tothe transistor M1. The transistor M1 comprises a first terminal coupledto the input voltage Vdd, a control terminal coupled to the outputterminal of the error amplifier EA1 and a second terminal outputting theoutput voltage Vout.

The voltage regulator unit 20″ converts the input voltage Vdd to theoutput voltage Vout by comparing the reference voltage Vref and thefeedback voltage Vbk from the switching-capacitor circuit 30A. Forexample, when the feedback voltage Vbk is higher than the referencevoltage Vref, the error amplifier EA1 lowers the voltage on the controlterminal of the transistor M1 such that the output voltage Vout isincreased. On the contrary, when the feedback voltage Vbk is lower thanthe reference voltage Vref, the error amplifier EA1 increases thevoltage on the control terminal of the transistor M1 such that theoutput voltage Vout is lowered. Thus, the voltage regulator unit 20″ canmaintain the output voltage Vout at a desired voltage level according tothe reference voltage Vref and the feedback voltage Vbk.

The switching-capacitor circuit 30A comprises capacitors C1 and C2 andswitching elements SW1˜SW4. The capacitor C1 has a first terminalcoupled to the output voltage Vout and a second terminal coupled to theswitching element SW2. The switching element SW1 has a first terminalcoupled to the first terminal of the capacitor C1, and a second terminalcoupled to the second terminal of the capacitor C1. The switchingelement SW2 has a first terminal coupled to the second terminal of thecapacitor C1 and a second terminal coupled a node ND1, in which thevoltage at the node ND1 serves as the feedback voltage Vbk. Theswitching element SW3 has a first terminal coupled to the node ND1 and asecond terminal coupled to the capacitor C2 and the switching elementSW4. The capacitor C2 has a first terminal coupled to the secondterminal of the switching element SW3 and a second terminal coupled to abias voltage (here a ground voltage Gnd is served as the bias voltage).The switching element SW4 has a first terminal coupled to the firstterminal of the capacitor C2 and a second terminal coupled to the groundvoltage Gnd.

FIG. 4 shows a control timing chart of the switching elements in theswitching-capacitor circuit shown in FIG. 3. Operations of theswitching-capacitor circuit 30A are described with reference to FIGS. 3and 4. As shown, during a time period t0˜t1, the switching elements SW1and SW4 are tuned off and the switching elements SW2 and SW3 are turnedon, the capacitors C1 and C2 extracts a division voltage from the outputvoltage Vout to serve as the feedback voltage Vbk (i.e., the voltage onthe node ND1). For example, the capacitors C1 and C2 extract thedivision voltage from the output voltage Vout by charge sharingtherebetween to serve as the feedback voltage Vbk. During a time periodt1˜t2, all switching elements SW1˜SW4 are turned off. Because theswitching elements SW2 and SW3 are turned off, the voltage at the nodeND1 (i.e., the feedback voltage Vbk) is maintained (i.e., the same asthe last time period t0˜t1). Then, during a time period t2˜t3, theswitching elements SW1 and SW4 are turned on and the switching elementsSW2 and SW3 are turned off, such that two terminals of the capacitor C1are both coupled to the output voltage Vout, and two terminals of thecapacitor C2 are both coupled to the ground voltage Gnd.

Next, during a time period t3˜t4, all switching elements SW1˜SW4 areturned off again. During a time period t4˜t5, the switching elements SW1and SW4 are tuned off and the switching elements SW2 and SW3 are turnedon, the capacitors C1 and C2 extracts a division voltage from the outputvoltage Vout again. Then, during a time period t5˜t6, the switchingelements SW1˜SW4 are turned off. Because the switching elements SW2 andSW3 are turned off, the voltage at the node ND1 (i.e., the feedbackvoltage Vbk) is maintained (i.e., the same as the last time periodt4˜t5).

During a time period t6˜t7, the switching elements SW1 and SW4 areturned on and the switching elements SW2 and SW3 are turned off, suchthat two terminals of the capacitor C1 are both coupled to the outputvoltage Vout, and two terminals of the capacitor C2 are both coupled tothe ground voltage Gnd both, and so on.

In this embodiment, the capacitor C1 and the switching elements SW1 andSW2 can be regarded as a first resistor and the capacitor C2 and theswitching elements SW3 and SW4 can be regarded as a second resistor.Equivalent resistance of the first and second resistors can beconsidered as T1/C11 and T2/C22 respectively, in which C11 representsthe capacitance of the capacitor C1, C22 represents the capacitance ofthe capacitor C2, T1 represents the duty period of the switching elementSW1 and T2 represents the duty period of the switching element SW4. Forexample, the resistance of 1MΩ can be obtained when the capacitor C1 is1 pF and the switching element SW1 is operated at 1 MHz (i.e., dutyperiod is 10⁻⁶ sec). Namely, the resistance of the first and secondresistors can be modified by different capacitances and different dutyperiod of switching elements SW1˜SW4.

FIG. 5 shows another embodiment of the voltage regulator. As shown, thevoltage regulator 400 is similar to the voltage regulator 300 shown inFIG. 3, except that a switching element SW5 is coupled between the nodeND1 and the second input terminal of the error amplifier EA1. FIG. 6shows a control timing chart of the switching elements in theswitching-capacitor circuit shown in FIG. 5. Operations of theswitching-capacitor circuit in the voltage regulator 400 are describedwith reference to FIGS. 5 and 6.

As shown, during a time period t0˜t1, the switching elements SW1 and SW4are tuned off and the switching elements SW2, SW3 and SW5 are turned on,the capacitors C1 and C2 extracts a division voltage from the outputvoltage Vout to serve the feedback voltage Vbk (i.e., the voltage on thenode ND1). At time t1, the switching elements SW1 and SW4 remain off andthe switching elements SW2 and SW3 remain on, and the switching elementSW5 is turned off. Hence, the voltage at the second input terminal ofthe error amplifier EA1 (i.e., the feedback voltage Vbk) is maintained(i.e., the same as the last time period t0˜t1).

At time period t2, the switching elements SW1, SW4 and SW5 remain offand the switching elements SW2 and SW3 are turned off. During a timeperiod t2˜t3, all switching elements SW1˜SW5 remain off. Then, during atime period t3˜t4, the switching elements SW2, SW3 and SW5 remain offand the switching elements SW1 and SW4 are turned on such that twoterminals of the capacitor C1 are both coupled to the output voltageVout, and two terminals of the capacitor C2 are both coupled to theground voltage Gnd both. Next, at time t4, the SW2, SW3 and SW5 remainoff and the switching elements SW1 and SW4 are turned off. Then, duringa time period t4˜t5, all switching elements SW1˜SW5 remain off. Theoperations during time period t5˜t9 is similar to that during the timeperiod t0˜t5, and so on.

FIG. 7 shows another embodiment of a voltage regulator. As shown, avoltage regulator 500 is similar to the voltage regulator 300 shown inFIG. 3, except that the capacitor C2 is replaced by a variable capacitorC3. The variable capacitor C3 comprises capacitors C3_0˜C3 _(—) n andswitching elements SWC_1˜SWC_n. The capacitor C3_0 is coupled between anode ND2 and the ground voltage Gnd, the capacitor C3_1 and theswitching element SWC_1 are connected in series between the node ND2 andthe ground voltage Gnd, the capacitor C3_2 and the switching elementSWC_2 are connected in series between the node ND2 and the groundvoltage Gnd, and so on. When the switching element SWC_1 is turned on,the capacitors C3_0 and C3_1 are connected in parallel and thecapacitance of the variable capacitor C3 is increased. When theswitching elements SWC_1˜SWC_2 are both turned on, the capacitorsC3_0˜C3_2 are connected in parallel and the capacitance of the variablecapacitor C3 is further increased, and so on. Namely, the more of theswitching elements SWC_1˜SWC_n are turned on, the larger the capacitanceof the variable capacitor C3. Operations of the voltage regulator 500are similar to that of the voltage regulator 300 shown in FIG. 3 andthus, are omitted for brevity. The voltage regulator 500 can adjustvoltage level of the output voltage Vout by tuning the capacitance ofthe variable capacitor C3.

FIG. 8 shows another embodiment of a voltage regulator. As shown, avoltage regulator 600 is similar to the voltage regulator 300 shown inFIG. 3, except that the switching-capacitor circuit 30A is replaced witha switching-capacitor circuit 30B. The switching-capacitor circuit 30Bcomprises switching elements SW6˜SW9 and capacitors C4˜C5. The switchingelement SW6 has a first terminal coupled to the output voltage Vout anda second terminal coupled to a node ND3. The capacitor C4 has a firstterminal coupled to the node ND3 and a second terminal coupled to theground voltage Gnd. The switching element SW7 has a first terminalcoupled to the node ND3 and a second terminal coupled to a node ND3″.The capacitor C5 has a first terminal coupled to the node ND3″ and asecond terminal coupled to the ground voltage Gnd. The switching elementSW8 has a first terminal coupled to the node ND3″ and a second terminalcoupled to the ground voltage Gnd. The switching element SW9 has a firstterminal coupled to the node ND3 and a second terminal coupled to thesecond terminal input terminal of the error amplifier EA1.

FIG. 9 shows a control timing chart of the switching elements in theswitching-capacitor circuit shown in FIG. 8. Operations of theswitching-capacitor circuit 30B are described with reference to FIGS. 8and 9.

As shown, during a time period t0˜t1, the switching elements SW6 and SW8are tuned off and the switching elements SW7 and SW9 are turned on, thecapacitors C1 and C2 perform a voltage-division to the output voltageVout to serve the feedback voltage Vbk. For example, the output voltageVout stored in the capacitor C4 charges the capacitor C5, i.e., chargesharing between capacitors C4 and C5 are executed, to extracts thedivision voltage of the output voltage Vout to serve as the feedbackvoltage Vbk.

At time t1, the switching elements SW6 and SW8 remain off and theswitching elements SW7 remains on, and the switching element SW9 isturned off. Hence, the voltage at the second input terminal of the erroramplifier EA1 (i.e., the feedback voltage Vbk) is maintained (i.e., thesame as the last time period t0˜t1). At time period t2, the switchingelements SW6, SW8 and SW9 remain off and the switching element SW7 isturned off. During a time period t2˜t3, all switching elements SW1˜SW5remain off.

Then, during a time period t3˜t4, the switching elements SW7 and SW9remain off and the switching elements SW6 and SW8 are turned on suchthat the capacitor C4 is charged by the output voltage Vout and twoterminals of the capacitor C5 are both coupled to the ground voltageGnd. Next, at time t4, the SW7 and SW9 remain off and the switchingelements SW6 and SW8 are turned off. Then, during a time period t4˜t5,all switching elements SW6˜SW9 remain off. The operations during timeperiod t5˜t9 are repeated.

In some embodiments, the capacitor C4 or the capacitor C5 can bereplaced with the variable capacitor C3 shown in FIG. 7 for adjustingthe output voltage Vout to a wanted voltage level. Because capacitanceper unit is increased more and more in advanced semiconductor processes,it is more efficient to replace the feedback resistor with capacitorsand switching elements and thus the layout area of the voltage regulatorcan be reduced. In some embodiment, the capacitors C1˜C5 or C3_0˜C3 _(—)n can also be implemented on the active devices during forming ofmetal-insulator-metal devices or metal-on-metal devices, and thus, thecapacitors C1˜C5 or C3_0˜C3 _(—) n do not increase a chip's layout area.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

What is claimed is:
 1. An electronic circuit, comprising: a voltageregulation unit converting an input voltage to an output voltage bycomparing a reference voltage and a feedback voltage; a first capacitorcomprising a first terminal coupled to the output voltage, and a secondterminal; a first switching element comprising a first terminal coupledto the first terminal of the first capacitor, and a second terminalcoupled to the second terminal of the first capacitor; a secondswitching element comprising a first terminal coupled to the secondterminal of the first capacitor and the second terminal of the firstswitching element, and a second terminal coupled to the voltageregulation unit; a third switching element comprising a first terminalcoupled to the second terminal of the second switching element, and asecond terminal; a second capacitor comprising a first terminal coupledto the second terminal of the third switching element, and a secondterminal coupled to a bias voltage, wherein the first and secondcapacitors extract a division voltage from the output voltage by chargesharing between the first and second capacitors to obtain the feedbackvoltage; and a fourth switching element comprising a first terminalcoupled to a first terminal of the second capacitor and the secondterminal of the third switching element, and a second terminal coupledto the bias voltage, wherein the charge sharing is accomplished throughswitching operations of the first, second, third and fourth switchingelements; wherein the division voltage is a voltage on a connectionpoint of the first and second capacitors, and the switching elements areswitched by non-overlapping clocks, such that the first and secondcapacitors are not connected at the connection point during a firstperiod and the first and second capacitors are connected at theconnection point to perform the charge sharing during a second perioddifferent from the first period; wherein one or more of: first andsecond terminals of the first capacitor are directly connected togetherthrough a switch element during the first period; or first and secondterminals of the second capacitor are directly connected togetherthrough a switch element during the first period.
 2. The electroniccircuit as claimed in claim 1, wherein the electronic circuit is avoltage regulator.
 3. The electronic circuit as claimed in claim 1,wherein one of the first and second capacitors is a variable capacitor.4. The electronic circuit as claimed in claim 1, wherein the voltageregulation unit is a switching-mode power supply, or a charge-pumpcircuit.
 5. The electronic circuit as claimed in claim 2, furthercomprises a fifth switching element comprises a first terminal coupledto the voltage regulation unit, and a second terminal coupled to thesecond terminal of the second switching element and the first terminalof the third switching element.
 6. An electronic circuit, comprising: avoltage regulation unit converting an input voltage to an output voltageby comparing a reference voltage and a feedback voltage; a firstswitching element comprising a first terminal coupled to the outputvoltage, and a second terminal; a first capacitor comprising a firstterminal coupled to the second terminal of the first switching element,and a second terminal coupled to a bias voltage; a second switchingelement comprising a first terminal coupled to the first terminal of thefirst capacitor and the second terminal of the first switching element,and a second terminal; a second capacitor comprising a first terminalcoupled to the second terminal of the second switching element, and asecond terminal coupled to the bias voltage, wherein the first andsecond capacitors extract a division voltage from the output voltage bycharge sharing between the first and second capacitors to obtain thefeedback voltage, and the charge sharing is through switching operationsof the switching elements; a third switching element comprising a firstterminal coupled to the second terminal of the second switching elementand the first terminal of the second capacitor, and a second terminalcoupled to the bias voltage; and a fourth switching element comprising afirst terminal coupled to the first terminal of the first capacitor andthe second terminal of the first switching element, and a secondterminal coupled to the voltage regulation unit, wherein the chargesharing is accomplished through switching operations of the first,second, third and fourth switching elements; wherein the divisionvoltage is a voltage on a connection point of the first and secondcapacitors, and the switching elements are switched by non-overlappingclocks, such that the first and second capacitors are not connected atthe connection point during a first period and the first and secondcapacitors are connected at the connection point to perform the chargesharing during a second period different from the first period; whereinone or more of: first and second terminals of the first capacitor aredirectly connected together through a switch element during the firstperiod; or first and second terminals of the second capacitor aredirectly connected together through a switch element during the firstperiod.